Natural Radiative Lifetimes Research Articles

Experimental and theoretical investigation of radiative lifetimes in neutral gallium

Using laser spectroscopic techniques the natural radiative lifetimes of 4s2n1s2S and 4s2n2d2D states of neutral gallium have been measured forn1 = 6 to 11 andn2 = 4 to 9. These states, as well as previously measured4s2np2P states, have been investigated theoretically using multi-configuration Hartree-Fock calculations. Oscillator strengths to all lower-lying states have been calculated and theoretical lifetimes of the investigated states evaluated. The2D sequence is strongly influenced by the 4s4p22D perturber, and strong cancellation effects in the radiative decay are observed both theoretically and experimentally.

Natural radiative lifetimes in the 5snd 1 D 2 series of SrI

Natural radiative lifetimes in the 5snd 1 D 2 series of SrI

Natural radiative lifetimes in the3sns S01and3snd D21sequences of magnesium

Natural radiative lifetimes have been determined in the determined in the $3\mathrm{sns} ^{1}S_{0} (n=4\ensuremath{-}15)$ and the $3\mathrm{snd} ^{1}D_{2} (n=3\ensuremath{-}15)$ sequences of Mg I employing a pulsed-laser system. The radiative lifetimes in the $^{1}S_{0}$ sequence and of the higher members in the $^{1}D_{2}$ sequence are unperturbed and scale as ${({n}^{*})}^{2.6}$ (where ${n}^{*}$ is the effective principal quantum number), while the lifetimes of the lower members in the $^{1}D_{2}$ sequence are perturbed by the doubly excited $3{p}^{2}$ configuration. The measured lifetimes are compared with available theoretical calculations, and a very good agreement is obtained.

Natural radiative lifetimes in the1 P 1 and1 F 3 sequences of Sr I

Natural radiative lifetimes in the1 P 1 and1 F 3 sequences of Sr I

FLUORESCENCE PROPERTIES OF C‐PHYCOCYANIN ISOLATED FROM A THERMOPHILIC CYANOBACTERIUM

Abstract The fluorescence lifetime of purified C‐phycocyanin from the thermophilic cyanobacterium, Phormidium laminosum (strain OH‐1‐p. Cl 1), was measured as 1.48 ± 0.06 ns using the technique of time‐correlated single‐photon counting under very weak excitation pulses. The natural radiative lifetime (∼6.1 ns) of the pigment was calculated by integrating the absorption spectrum using the Strickler–Berg equation. From these two lifetimes we calculate a fluorescence quantum yield of ∼0.24 which is very close to the value ∼0.22 which we measure relative to the known value of cresyl violet in methanol. Both the fluorescence lifetime and the quantum yield of the pigment from this organism are lower than most previous values reported in the literature. We conclude that our lower values are not due to high light intensity, pH, buffer, concentration, instrumentation artifacts, aggregation effects or the thermophilic nature of the organism. Instead, we suggest that the photophysical properties of C‐phycocyanin are species dependent, perhaps due to the specific molecular environment of the tetrapyrrole.

Natural Radiative Lifetimes and Stark-Shift Parameters in the 4p2 Configuration in Ca I

The radiative lifetimes in the doubly excited 4p2 configuration in Ca were determined using the delayed coincidence technique. The measured states were populated either with two-step laser excitation from the 4s2 1S0 ground state or with single-step excitation starting from a metastable state. The metastable states were populated by collisions in a discharge. The following lifetime values were obtained: τ(4p2 1D2) = 16.3(20) ns, τ(4p2 1S0) = 14.4(7) ns and τ(4p2 3P0,1,2) = 6.9(4) ns. Stark shift parameters in the same configuration were measured using an atomic beam passing between electric field plates. The following results were obtained: α0(4p2 1S0) = -32.2(16) MHz (cm/kV)2, α0(4p2 1D2) = 1.8(2) MHz (cm/kV)2 and α2(4p2 1D2) = 1.15(10) MHz (cm/kV)2. Additional measurements yielded τ(4s5f1F3) = 60(3) ns, τ(4s4d3D1,2,3) = 13.0(5) ns and α0 (4s6s 1S0) = 6.98(35) MHz (cm/kV)2.

Natural radiative lifetimes in the2S1/2 and2D5/2,3/2 sequences of aluminum

Natural radiative lifetimes have been measured for the 3s2ns2S1/2 (n≦10) and 3s2nd2D5/2,3/2 (n≦11) sequences of aluminum using pulsed laser excitation of an atomic beam. The investigated states were populated from the ground configuration using UV pulses of wavelength down to 210 nm produced by a Nd: YAG- or an excimer-pumped dye-laser system. TheS-state lifetimes increase regularily with increasing principal quantum number but this is not the case for theD sequence.

Lifetime measurements in theS122andD32,522sequences of indium

Natural radiative lifetimes in the $5{s}^{2}\mathrm{ns}^{2}S_{\frac{1}{2}}$ and $5{s}^{2}\mathrm{nd}^{2}D_{\frac{3}{2},\frac{5}{2}}$ ($n\ensuremath{\le}20$) sequences of indium have been measured using pulsed laser excitation of an atomic beam. The uv pulses were produced by a YAG-pumped, or alternatively, an excimer-pumped dye-laser system. While the $S$-state lifetimes show a normal ${({n}^{*})}^{3}$ behavior, the $D$ sequences are strongly perturbed. The lifetimes of the $5s5{p}^{2}^{4}P$ states were found to be $J$ dependent.

Natural radiative lifetimes in the interacting5sndD21,3sequences in Sr

Natural radiative lifetimes have been determined in the $5snd^{1,3}D_{2}$ sequences of strontium in the perturbed region around $n=15$. Stepwise laser excitations and pulse modulation of a cw dye-laser beam were employed. A plot of the measured lifetime values versus the effective quantum number reveals complex configuration interaction.

Natural radiative lifetimes and hyperfine structure of the [formula omitted] levels of gallium

Natural radiative lifetimes and the signs of previously determined hyperfine coupling constants were determined for the 4s 26p 2P 3 2 , 1 2 levels of gallium. The lifetimes were found to be 167(4) and 172(9) ns, respectively. In addition, the quadrupole moments of 69Ga [0.17(3) b] and 71Ga [0.10(2) b] were deduced, and the isotope shifts in the 639.7 and 641.3 nm Ga lines were determined.

Determination of the lifetime of the mercury 6 3P 1 state

A pulsed tunable dye laser was used for a high resolution experimental study of mercury fluorescence from the 6 3 P 1 state. The output of the dye laser was frequency doubled into the 253.7 nm region using a potassium penta-borate crystal. Exponential decays were observed for each of the five individual components of the hyperfine structure separately and the effects of the trapping of resonance radiation on the observed lifetime of the 6 3 P 1 state of mercury were investigated for each resolvable component. Within experimental error, the natural radiative lifetime of the 6 3 P 1 state was found to be independent of the hyperfine component irradiated and a value of 122±2 nsec was obtained, consistent with results found by other methods.

Natural radiative lifetimes in the perturbed 6snd 1 D 2 sequence of barium

Natural radiative lifetimes in the perturbed 6s n s1D2 (n=12−30) sequence of barium have been measured using the PUMOLS (PUlse-MOdulated Laser Spectroscopy) method, which incorporates pulse-modulation of a CW dye-laser beam and delayed coincidence techniques. Principal perturbers are the 5d 7d3F2 and1D2 states. Lifetimes were also measured for these shortlived valence states, which through configuration mixing cause drastic decreases in lifetime values in the region of perturbation of the 6s n d1D2 sequence. Two-step laser excitation from the ground 6s21S0 state via the 6s 6p1P1 state was employed. Special care was taken to determine the influence of black-body radiation transitions on the measured lifetimes.

Photophysics of N,N-dimethyldihydrophenazine and benzoannelated analogs. Structurally dependent excited-state hierarchy

Abstract : Absorption and fluorescence spectra, fluorescence lifetimes, and fluorescence quantum yields for 5,10-dimethyl-5,10-dihydrophenazine (DMP), 9,14-dimethyl-9,14-dihydrodibenzoA,C phenzaine (DMAC), 9,14-dimethyl-9,14-dihydrophenanthro4,5-ABCphenazine (DMPP) and 6,13-dimethyl-6,13-dihydrobibenzoB,Iphenazine (DBMI) have been measured in benzene solution at room temperature. The excited state behavior of DMP, DMAC, and DMPP is similar. The long natural radiative lifetimes and large separation between absorption and emission maxima suggest that the first transition is symmetry forbidden. DMBI is unique in the series with a comparatively short natural radiative lifetimes and a relatively small separation between absorption and emission maxima. These results, in conjunction with PPP calculations, reveal a different hierarchy of electronic states for DMBI, such that the first transition is strongly allowed. (Author)

Lifetime measurements for excited states of rare-earth atoms using pulse modulation of a cw dye-laser beam

By pulse-modulating a cw dye-laser beam and employing the delayed-coincidence technique, we have determined the natural radiative lifetimes of a number of atomic states in rare-earth atoms Eu, Dy, and Yb. In the measurements, which were performed on an atomic beam, exponential decay curves with good statistics were obtained using short measuring times. The general features of the technique are discussed. When possible, oscillator strengths are deduced and compared with literature values.

Determination of natural radiative lifetimes and Land� factors for highly excitedF states in cesium

Natural radiative lifetimes and LandegJ factors for several highly excitedF states in cesium were measured using time-resolved fluorescence spectroscopy. TheF states were excited from the 52D5/2 state with a pulse-modulated CW dye laser, and the delayed-coincidence method was employed to record decay curves, which in some experiments exhibited Zeeman quantum beats. A further CW dye laser was used to produce the necessary population in the 52D5/2 state. The lifetimes in the sequence 11–162F7/2 follow anx scaling law withx=2.76 and the Lande factors agree with the predicted value, 1.143.

Radiative lifetimes of highly excited F states in rubidium

Measurements have been made of the natural radiative lifetimes of rubidium highly excited (9<or=n<or=21) F states. The nF states are populated using super-radiant cascading effects in rubidium Rydberg levels. Lifetimes calculated by the Coulomb approximation method agree with our experimental data.

Determination of natural radiative lifetimes for highly excited P states in rubidium

The natural radiative lifetimes of highly excited (12 ⩽ n ⩽ 22) P states in rubidium have been measured. They exhibit a near-hydrogenic behaviour with, however, some deriation of the absolute values from the available theoretical calculations.

Solvent and temperature effects on natural radiative lifetimes of some substituted polyenes

The extent to which the concept of a natural radiative lifetime (τ0) can be used as an indicator of what is taking place on the molecular level as the solvent or temperature changes is considered. The observation is made that since the universal solvent shift can be explained by perturbation theory, this indicates that the fluorescing state is really a mixture of states of the isolated molecule. With this as a basis, a simplified coupling model is introduced and resolvent techniques are used to solve for the time-dependence of the fluorescing state as a function of the solvent–solute interaction strength. The results indicate that much of the dependence of τ0 on the solvent and temperature for the retinols and diphenylpolyenes may be due to the state mixing introduced by the solvent perturbations. In these molecules as the strength of solvent induced state mixing increases, τ0 decreases. The temperature effect is such that τ0 decreases as T decreases because of an increase in solvent perturbation correlated to density increase.

Determination of natural radiative lifetimes for S and D states in rubidium and cesium using a pulsed dye laser

Using delayed-coincidence techniques we have measured the natural radiative lifetimes of several S and D states in Rb and Cs. The states were excited by a pulsed dye laser from the first P state, populated using an rf discharge lamp.

Excitation of the C 3Πu state of N2 by electron impact

The λ=3371 Å spectral band of the C 3Πu→B 3Πg (v′=0, v″=0) second positive system is investigated using time-resolved spectroscopy with electron beam pulse widths of 100 nsec, 260 nsec, and 5 μsec. Lifetime data for the v′=0 vibrational level of the C 3Πu electronic state are obtained for incident electron energies and N2 gas pressures in the range 25–200 eV and 2–380 mtorr, respectively. In the case of the 260 nsec electron pulse, a single radiative decay component is observed which exhibits a dependence upon electron impact energy. However, in the case of a 5 μsec excitation pulse the resulting radiative decay is observed to consist of two decay components. The short-lived component is identified as the primary C 3Πu state excitation, while the long-lived component is identified as the radiative cascade contribution from higher electronic states, including possibly the metastable E 3Σ+g state. When the long-lived cascade contribution is subtracted from the total C 3Πu population, the C state natural radiative lifetime becomes independent of energy. In addition, the lifetime is observed to be independent of N2 gas pressure over the pressure range ∼2–380 mtorr.